Intelligent transportation systems (ITS), sometimes known as intelligent highways, intelligent vehicles, or driver assistance systems, have engaged the interest of transportation planners for some years. A few applications have already been deployed, and many others await. Application areas include vehicle location, warning vehicles of the actions of other vehicles, alerting drivers to environmental and infrastructure conditions, traffic control, and others.
One of the barriers to ITS deployment is the need for wireless data communications over medium ranges, perhaps 300-2000 meters. However, recent work has produced specifications for a number of suitable and inexpensive communications protocols. For example, the Institute of Electrical and Electronic Engineers (IEEE) has adopted a packet-based low-latency protocol operating at 5.9 GHz, known as IEEE 802.11p, or Dedicated Short Range Communications (DSRC).
A remaining problem, however, concerns the sensing of vehicle positions with high accuracy and yet at a cost low enough to be affordable for every vehicle. The Global Positioning System (GPS) has become widespread, although it is still on the high end of an acceptable cost range. However, a number of ITS applications require accuracy that may lie beyond the ability of GPS and similar navigation aids. For example, an ITS application may wish to alert a driver in one lane of a roadway, while not alerting the driver of a vehicle a meter or so away in the next lane. Infrastructure units, such as traffic-light controllers, may wish to know which highway lane a vehicle is in. Besides accuracy or resolution limitations, GPS may be unavailable or unreliable in some areas. Overpasses may block satellite signal reception. Tall buildings in downtown areas may lead to multipath distortion. Roadside vehicle sensors such as radar are expensive, energy-intensive, and may also be subject to signal blockage from nearer vehicles or other objects. Active in-roadway sensors such as current-loop detectors are commonly used today for applications such as vehicle sensing at traffic lights and other signals. These systems, however, are prone to circuit faults in the pavement and other failures.
Another problem is that conventional intelligent highway systems place a vehicle at only a single point on a roadway. This is not sufficient for a number of ITS applications. For example, a vehicle whose front is 50 feet behind the front of a second vehicle in the next lane might merge into that lane safely if the second vehicle is a passenger car. However, a collision may result if the second vehicle is a tandem-trailer truck. That is, conventional systems are hampered in that they are not able to determine the total extent of road space that a vehicle actually occupies.